I guess that phrase "Simeon absorbed within Judah" doesn't imply Simeon's descendants lost their identity.
An attempt to create a new Kingdom of Israel in Ukraine at the beginning of the 1st millennium (The Thirteen Tribe: The Khazar Empire and its Heritage, by Arthur Koestler) shows Simeon's descendants claiming their ancestry outside of Judah and Levy.
But, lets play the game that Simeon was attached as part of Judah, even when -as an example- in Judges 1:3 only says: And Judah said unto Simeon his brother, Come up with me into my lot, that we may fight against the Canaanites; and I likewise will go with thee into thy lot. So Simeon went with him. No assimilation implied.
The blessings of Moses ignored Simeon but when it was about Joseph, Moses clarifies the blessings to his two sons, Ephraim and Manasseh, and here you can have two tribes instead of one, and at the end you still have your "ten lost tribes".